1. Field Of The Invention
The present invention relates to a polyamide resin composition. More particularly, the present invention is concerned with a polyamide resin composition comprising a melt-kneaded product of (A) a polyamide; (B) a polyphenylene ether; (C) a styrene polymer; and (D) a compound having in a molecule thereof a carbon-to-carbon double bond and at least one functional group selected from the group consisting of a carboxylic acid group, an acid anhydride group, an epoxy group, an amino group and a hydroxyl group, wherein the polyamide (A) is present as a continuous phase in which the polyphenylene ether (B) and the styrene polymer (C) are dispersed individually, independently or in mixture thereof to form a dispersion phase having an average particle diameter of 5 .mu.m or less, and wherein the polyphenylene ether (B) and the styrene polymer (C) are present in a specific (B)/(C) weight ratio, and the styrene polymer (C) in the melt-kneaded product has a specific reduced viscosity. The polyamide resin composition of the present invention has various excellent properties, such as excellent mechanical properties, heat resistance, molding processability, light stability and weatherability. Further, the polyamide resin composition of the present invention fully enjoys the advantageous features of a polyamide/polyphenylene ether alloy, namely, high resistance to a dimensional change and to a lowering of stiffness when exposed to water, and high chemical resistance. Therefore, the polyamide resin composition of the present invention is useful for producing various shaped resin articles, such as exterior and interior parts of automobiles, electronic parts, electric parts, civil engineering materials and construction materials.
2. Discussion Of Related Art
Polyphenylene ether resins (hereinafter frequently referred to as "PPE resins") have excellent dimensional stability, electrical properties, heat distortion resistance under a high load, water resistance, etc. The PPE resins are widely utilized in the form of a blend with a styrene polymer for commercial uses. Polyphenylene ether resins, however, have serious disadvantages in that they have poor oil resistance and molding flow properties as compared to other types of resins.
On the other hand, polyamide resins have excellent mechanical strength, oil resistance, heat resistance, etc., and have been utilized in large quantities as one of the most typical engineering plastics. However, polyamide resins have disadvantages in that they are poor in some properties, such as dimensional stability, insusceptibility to moisture absorption, heat distortion resistance under a high load, and impact resistance in the dry state, as compared to other types of resins.
Accordingly, blending of both of these resins (the blending of the resins being conducted so as to be accompanied with reactions therebetween) has been attempted in order to attain effective utilization of the respective excellent properties inherent in these resins and to compensate for the respective disadvantages of these resins. Along with such attempts, various compositions have been proposed and put into practical use.
For example, a resin composition has been proposed which employs a polyamide; a polyphenylene ether; optionally an elastomer; and a copolymer of styrene and an .alpha., .beta.-unsaturated carboxylic acid or an anhydride thereof as a compatibility agent for the polyamide and polyphenylene ether, wherein the polyamide is present as a continuous phase and the polyphenylene ether is present as a dispersion phase (see Examined Japanese Patent Application Publication No. 59-33614 corresponding to U.S. Pat. No. 4,339,376). This resin composition is advantageous in that it has the excellent oil resistance inherent in a polyamide and the heat resistance inherent in a polyphenylene ether. However, this resin composition has drawbacks in that it is poor in molding flow properties and light stability thereof and in appearance of a glass fiber-reinforced shaped resin article produced therefrom.
Another resin composition has been proposed which employs, as a compatibility agent for a polyamide and polyphenylene ether, a graft polymer obtained by reacting a polyamide, a polyphenylene ether, and an .alpha., .beta.-unsaturated carboxylic acid or an anhydride thereof to thereby link the polyamide and the polyphenylene ether to each other. This resin composition contains a polyamide; a polyphenylene ether; this compatibility agent; and optionally a rubbery polymer, wherein the polyamide is present as a continuous phase and the polyphenylene ether is present as a dispersion phase (see Examined Japanese Patent Application Publication No. 4-28748, U.S. Pat. No. 4,888,397, U.S. Pat. No. 4,654,405, EP 226910, U.S. Pat. No. 4,772,664, EP 269748, and U.S. Pat. No. 4,943,399). This resin composition is improved with respect to various properties, such as heat resistance and impact resistance. In the above-mentioned publications, it is described that a polystyrene may be incorporated into this resin composition. However, when a polystyrene is incorporated into this resin composition, the impact resistance of the resin composition is drastically lowered, to thereby make it impossible to practically use the resin composition.
As described above, there is no conventional polyamide resin composition which has a good balance of various desired properties, such as excellent mechanical properties, heat resistance, molding flow properties, light stability, good appearance of a shaped article, etc. Therefore, it has been strongly desired to develop a practically useful polyamide resin composition which is free from the above-mentioned problems of the prior art and which has all of the various desired properties simultaneously.